This invention relates generally to rotating seals and more particularly to a rotating seal for use as the forward outer seal of a gas turbine engine.
A gas turbine engine includes a compressor that provides pressurized air to a combustor wherein the air is mixed with fuel and ignited for generating hot combustion gases. These gases flow downstream to one or more turbines that extract energy therefrom to power the compressor and provide useful work such as powering an aircraft in flight. Aircraft engines ordinarily include a stationary turbine nozzle disposed at the outlet of the combustor for channeling combustion gases into the first stage turbine rotor disposed downstream thereof. The turbine nozzle directs the combustion gases in such a manner that the turbine blades can do work.
Typically, a forward outer seal is provided between the stationary turbine nozzle and the first stage turbine rotor for sealing the compressor discharge air that is bled off for cooling purposes from the hot gases in the turbine flow path. However, in most high pressure turbines, the forward outer seal requires use of a number of by-pass holes which permit a flow of cooling air into the forward wheel cavity between the turbine nozzle and the first stage turbine rotor. This air purges the forward wheel cavity to ensure against hot gas ingestion. A failure to maintain adequate purge flow can lead to significantly reduced part life of adjacent components.
Conventional forward outer seals comprise a rotating labyrinth seal made up of a rotating seal element and a static seal element. The rotating element has a number of thin, tooth-like projections extending radially from a relatively thicker base toward the static element. The static element is normally of a honeycomb material. These seal elements are generally situated circumferentially about the longitudinal centerline axis of the engine and are positioned with a small radial gap therebetween to permit assembly of the various components. When the gas turbine engine is operated, the rotating element expands radially and rubs into the static element, thereby creating the seal. During new engine operation, the labyrinth seal experiences little or no leakage. Thus, by-pass holes are required to ensure adequate purge flow into the forward wheel cavity. Over time, however, continued operation of the engine will result in gradual deterioration of the seal elements. This means that more cooling air will leak through the labyrinth seal into the forward wheel cavity and supplement the purge flow through the by-pass holes. Eventually, the amount of air leaking through the labyrinth seal will be sufficient to purge the forward wheel cavity, reducing, or even eliminating, the need for the by-pass holes. But because of the presence of the by-pass holes, which are necessary during new engine operation, the wheel cavity purge flow is greater than necessary, which is detrimental to overall engine performance.
Accordingly, there is a need for a turbine forward outer seal that provides adequate purge of the forward wheel cavity during initial engine start up and reduces the level of by-pass air as the seal deteriorates.
The above-mentioned needs are met by the present invention which provides a rotating seal including a rotating member arranged to rotate about an axis and having at least one annular projection extending radially outwardly therefrom, and a stator element having a first surface arranged to contact the projection. The stator element includes at least one slot formed in the first surface, the slot axially traversing the projection so as to allow a flow of purge air to pass. More than one such slot can be used, and each slot is preferably angled circumferentially in the direction of rotation of the rotating member.
When utilized as the forward outer seal in a gas turbine engine, the rotating seal of the present invention eliminates the need for conventional by-pass holes, and by better matching the amount of purge flow to the engine""s forward wheel cavity to the seal deterioration, the present invention improves engine performance over a longer period of operation.
Other objects and advantages of the present invention will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.